CLASSIFICATION. 13 



every department of created existence, for the purpose of 

 assisting the memory to retain the names, forms, and habits 

 of the subjects investigated ; to recur to them readily ; and 

 in speaking or writing of them to employ incidental re- 

 ferences, without needless circumlocution. 



In Zoology, or that branch of Natural History which 

 relates to the Animal Kingdom, the process by which syste- 

 matic arrangement is arrived at, commences with an exami- 

 nation of the almost innumerable species of which it is com- 

 posed. A number of these species, having slight differences, 

 but a strong general resemblance, form a Genus ; the Genera 

 most nearly allied are united into a Family ; several families 

 into an Order ; several Orders into a Class ; and these classes 

 again are arranged under four principal divisions, called 

 Sub-kingdoms. 



The following is an outline of the arrangement adopted 

 in the succeeding pages. 



The entire Animal Kingdom, it has been already observed, 

 is divided into four Sub-kingdoms ; and- these comprehend, 

 respectively, the Yertebrated, Articulated, Molluscous, and 

 Radiated animals. 



The Yertebrated sub-kingdom, containing those animals 

 which possess a jointed spinal column (and with which alone 



